1. Field of the Invention
The invention relates to circuitry for use with an air data computer, more particularly, for calibration free analog circuitry used to monitor a temperature probe.
2. Discussion of the Prior Art
Modern aircraft use temperature responsive resistance probes to monitor the temperature of the air through which the aircraft fly. The probe connects through a wiring harness and processing circuitry to the plane's air data computer (ADC). Typical prior art circuitry used for temperature monitoring using a resistive probe, in combination with air data computers for aviation applications, such as in the F/A-18, utilize discrete analog circuitry. Such prior art devices must be calibrated at final test, and at any time during the service of the ADC that excessive error is detected. Such calibration requires bench calibration using a precision voltmeter. Calibration takes one to two hours during manufacture. Moreover, the prior art devices require a larger number of parts, more expensive parts and more circuit board space than does a circuit in accordance with the invention. Too, the manufacturing costs of prior art devices are higher than those of the invention which uses several relatively low cost ratio-metric resistors, i.e., resistors within integrated circuits, and only a few costlier absolute resistors. Significantly, the circuitry of the invention provides essentially 25% greater accuracy than the prior art discrete analog devices. The circuit of the invention requires no calibration with use since essential components are generally paired, age together and any errors from aging substantially offset one another.